Many combined cycle power plants using a gas turbine and steam turbine operating on the gases exiting the gas turbine have been used lately. The capacity of such combined cycle power plants is usually about 100-200 MW.
The possibility of employing both a diesel engine and an organic Rankine cycle (ORC) power unit to increase thermal efficiency in a combined cycle power plant configuration has been suggested. The use of both a diesel engine and an ORC power unit in a combined cycle power plant presents power plant designers with difficulties in terms of integrating the two different, simultaneously operating thermodynamic cycles. Firstly, a diesel engine is an internal combustion engine, while an ORC power unit is an external combustion engine. These two thermodynamic cycles therefore require different regimes of operation. That is, a diesel engine can be designed to operate at certain, fixed rotational speeds or within a given range depending on the use. The efficiency of an ORC power unit, on the other hand, is dependent on the rotational speed of the turbine and operates more efficiently at an optimal rotational speed. Secondly, diesel engines which are adapted for standby and peaking applications are able to start operating when cold and generate a maximum amount of power in only a few seconds. However, an ORC power unit cannot generate power prior to an initial start-up period of approximately 20-25 minutes during which hot vapors for driving the turbine need to be generated. Also, the turbine of a low-capacity ORC power unit is lubricated by means of the working fluid condensate, and a start-up period is needed to properly lubricate the turbine.
Another difference between diesel engines and an ORC power unit is that a diesel engine has a significantly greater number of components that need to be controlled and maintained than that of an ORC power unit. With respect to a diesel engine, at least the following components need to be controlled: the fuel injector, the governor for regulating the amount and pressure of fuel to be injected, the camshaft to provide the proper timing of fuel injection, and turbocharging systems for boosting power, improving combustion efficiency, and reducing emissions. J. Anderson in “Clean Diesel Generators—The Future is Here,” Power Topic #301, Cummins Power Generation describes that the control strategies of a diesel engine are aimed to optimize the combustion process while producing the least amount of both NOx and particulates per unit of power output, these strategies including the use of electronic engine controls, such as electronic sensors and microprocessor-based controls, and electronic injection systems. In an ORC power unit, an optimal power output can be achieved by controlling substantially only the fuel burner that produces and supplies to the vaporizer a given amount combustion gases from the fuel supplied to the fuel burner, when the power plant is not a combined cycle, and the rotational speed of the turbine.
U.S. Pat. Nos. 4,590,384 and 6,526,754, the disclosures of which are hereby incorporated by reference, disclose a combined cycle power plant by which hot exhaust gases of a diesel engine are used to vaporize organic working fluid of an ORC power unit. While such plants can produce approximately 10-20% additional power with respect to a conventional diesel engine, it would be desirable to further increase the power output of the plant. U.S. Pat. No. 6,883,328, the disclosure of which is also hereby incorporated by reference, on the other hand, discloses a combined cycle power plant wherein the hot exhaust gases of the diesel engine are used to produce vaporized working fluid of ORC power unit and wherein in addition, the ORC power unit can produce 100% of power produced once the diesel engine stops operation. U.S. patent application Ser. No. 10/849,502, the disclosure of which is also hereby incorporated by reference, which claims priority to Israel Patent Application 158989, and which is a Continuation-in-Part patent application of U.S. patent application Ser. No. 10/152,356, which matured into U.S. Pat. No. 6,883,328, mentioned above, discloses an ORC power unit operating from the exhaust heat gases of a high temperature fuel cell system such as a molten carbonate fuel cell system.
As described above, the control of each of a diesel engine and an ORC power unit is different, and at times, may be contradictory; for example, a diesel engine may be controlled to achieve a fast start-up, while such a control is not feasible for an ORC power unit. Prior art combined cycle power plants comprising both a diesel engine and an ORC power unit have employed a separate control system for each of the thermodynamic cycles due to their lack of control compatibility. When the combined cycle power plant has a capacity greater than, e.g. about 5 MW, a power plant employing two separate control systems, interconnections between the engine generator(s) and an ORC power unit, and expensive exhaust interconnections from the diesel engines may be cost effective due to the use of heat recovery cycles. However, the cost effectiveness of such a capacity combined cycle power plant employing two separate control systems for the start-up, synchronization, and continuous control of both the diesel engine and ORC power unit is lacking.
There is therefore a need for a single control system for a combined cycle power system by which hot exhaust gases of an engine generator are used to vaporize the organic working fluid of an ORC power unit.
It is an object of the present invention to provide an integrated engine generator Rankine cycle power system, especially one having a capacity of less than about 5 MW, of an increased efficiency of the use of the power output.
It is an additional object of the present invention to provide an integrated engine generator Rankine cycle power system having a single control system.
Other objects and advantages of the invention will become apparent as the description proceeds.